Reduce output from singal generator

Sunsun22 · 5th February 2010, 09:01 AM

My digital oscilloscopte has a 3V 1KHz output. I used it to feed into my new phono amp (loading 200 ohms, 0.55mV sensitivity) but the output waveform is distorted. I can see there are at least 3 reasons:

1. The RIAA network distorted the output waveform - I can build an inverse RIAA network to correct this.

2. The phono amp is having distortion - I would like to know this.

3. The output at 3V is too high.

Can anyone teach me how can I calculate/use a resistor to lower the 3V to 0.55mV?

Speedskater · 6th February 2010, 02:35 PM

It's probably not an "Oscilloscope" that you are using. The "scope" part of the word means - a device for seeing or looking. Your picture represents a oscilloscope display.

The signal is generated by an "Oscillator" circuit.
To design the best voltage reducing pad circuit, one should know the output impedance of the oscillator circuit.

TubeMack · 6th February 2010, 03:26 PM

Quote:

Originally Posted by Speedskater

It's probably not an "Oscilloscope" that you are using. The "scope" part of the word means - a device for seeing or looking. Your picture represents a oscilloscope display.

The signal is generated by an "Oscillator" circuit.
To design the best voltage reducing pad circuit, one should know the output impedance of the oscillator circuit.

Hmmmm, maybe. He could be using the probe compensation output from the ocsilloscope. Never say never.

cliffyk · 12th February 2010, 10:51 PM

The probe compensation signal from your 'scope likely has a 1kΩ or so source impedance, and you are feeding a 200Ω load. This will reduce the signal somewhat (3.0V /1200Ω * 200Ω = 0.5V) however the phono input's sensitivity

You are feeding a 3.0V signal into an input with a 0.55mV sensitivity, basically overdriving it by a factor of 10--and hence the distortion.

Try using a 1.2MΩ resistor in series with the compensation signal, that should get the output down to 0.50mV or so

star882 · 13th February 2010, 01:28 AM

If you have a good sound card, use Baudline for testing. Use a voltage divider to reduce the signal voltage.
baudline signal analyzer - FFT spectrogram

5th February 2010, 09:01 AM	#1
Sunsun22 diyAudio Member Join Date: Jul 2004 Location: Hong Kong	Reduce output from singal generator My digital oscilloscopte has a 3V 1KHz output. I used it to feed into my new phono amp (loading 200 ohms, 0.55mV sensitivity) but the output waveform is distorted. I can see there are at least 3 reasons: 1. The RIAA network distorted the output waveform - I can build an inverse RIAA network to correct this. 2. The phono amp is having distortion - I would like to know this. 3. The output at 3V is too high. Can anyone teach me how can I calculate/use a resistor to lower the 3V to 0.55mV?

6th February 2010, 02:35 PM	#2
Speedskater diyAudio Member Join Date: Sep 2002 Location: Lakewood, Ohio	It's probably not an "Oscilloscope" that you are using. The "scope" part of the word means - a device for seeing or looking. Your picture represents a oscilloscope display. The signal is generated by an "Oscillator" circuit. To design the best voltage reducing pad circuit, one should know the output impedance of the oscillator circuit. __________________ Kevin

13th February 2010, 01:28 AM	#5
star882 diyAudio Member Join Date: Mar 2007	If you have a good sound card, use Baudline for testing. Use a voltage divider to reduce the signal voltage. baudline signal analyzer - FFT spectrogram __________________ "Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!

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12th February 2010, 10:51 PM	#4
cliffyk diyAudio Member Join Date: Nov 2009	The probe compensation signal from your 'scope likely has a 1kΩ or so source impedance, and you are feeding a 200Ω load. This will reduce the signal somewhat (3.0V /1200Ω * 200Ω = 0.5V) however the phono input's sensitivity You are feeding a 3.0V signal into an input with a 0.55mV sensitivity, basically overdriving it by a factor of 10--and hence the distortion. Try using a 1.2MΩ resistor in series with the compensation signal, that should get the output down to 0.50mV or so

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